02, is conducive to the reliability of the lead is very short: reduce the distributed inductance and capacitance, improve the anti-interference ability and circuit speed high mechanical strength: improve the circuit resistance to vibration and impact ability Good assembly consistency: high yield, small parameter dispersion

03, is not conducive to the reliability of the material mismatch increase: some ceramic substrate SMT components (such as some resistors, capacitors, leadless chip carrier LCC) and PCB substrate epoxy glass thermal expansion coefficient does not match, resulting in thermal stress failure is easier to pollution: SMT components and PCB board is not easy to clean, easy to stay in the flux of pollutants, the need to use special treatment methods surface mount reliability is far more good than bad, currently accounted for 90% of the proportion

04. Comparison of packaging materials

• Plastic package

Advantages: low cost (about 55% of ceramic package), light weight (about 1/2 of ceramic package), a large number of pins, weak high-frequency parasitic effect, easy to automate production. Disadvantages: poor air tightness, moisture absorption, not easy to heat, easy to age, sensitive to static electricity. Applicability: Most semiconductor discrete devices and integrated circuit conventional products.

• Ceramic package

Advantages: good air tightness, strong heat dissipation (high thermal conductivity), good high-frequency insulation performance, large power, high wiring density. Disadvantages: High cost. Applicability: Aviation, aerospace, military and other high-end markets.

• Metal package

Advantages: good air tightness, strong heat dissipation, electromagnetic shielding capability, high reliability. Disadvantages: High cost, limited number of pins. Applicability: Small scale highly reliable devices. It is usually called a non-airtight package, and ceramic and metal are airtight packages.

• Moisture absorption problem

The epoxy resin material used in plastic packaging has moisture absorption, and moisture is easily adsorbed on its surface. Water vapor can cause creep of the plastic sealing material itself, and if it invades the inside of the chip, it can lead to corrosion and surface contamination.

• Air tightness problem

The difference between the thermal expansion coefficient of plastic tube shell and metal lead frame, semiconductor chip and other materials is much larger (compared with ceramic and metal tube shell)→ temperature change will produce considerable mechanical stress at the material interface → gap at the interface → resulting in air tightness deterioration of water vapor accumulation at the gap → rapid vaporization and expansion when the temperature rises → interface stress further increases → it is possible to make plastic Seal burst (" popcorn "effect) PCB reflow welding temperature can rise to 205 ~ 250℃ within 5 ~ 40s, the rise gradient of 1 ~ 2℃/s, easy to produce the above effect.

• Temperature adaptability problem

The glass transition temperature of the plastic sealing material is 130 ~ 160℃, and the plastic sealing material will soften after exceeding this temperature, which also has an adverse effect on the air tightness. The temperature range of commercial plastic encapsulation devices is generally 0~ 70℃, -40~+85℃, -40~+ 125℃, and it is difficult to reach the military temperature range of -55~+125℃.

33 Golden Rules of Electronic component procurement

one Prevent suppliers from quoting in small units of measurement, thereby reducing your sensitivity to price.

2. The exact number of decimal points on the quotation should be determined according to the quantity purchased.

3. When analyzing and reviewing quotations, use the currency unit you use most often or are most familiar with. If RMB appreciates, what price should we quote for imports? In foreign currency; If the RMB depreciates, what price should we use for imports? Local currency)

4. From the point of view of quotation unit and method, we should try our best to quote in the most favorable way for us.

5. The quotation of the split should pay special attention to the quotation strategy and way of breaking the whole into pieces. (The so-called breaking into pieces is that there is a decimal point carry in each part of the split offer. Suppliers do a little more here, a little more there, and the whole thing goes up. This is also a problem that can easily occur in the "price list of supporting products" which is subdivided into many items.)

6. Quote according to the purchaser's cost structure. (When purchasing large quantities of products, the format of the quotation sheet should be done in accordance with the requirements of the procurement, that is, the supplier should be asked to quote in accordance with our unified quotation method and quotation format, including the cost calculation method should be unified in accordance with our requirements, which is very important. This will help you analyze supplier quotes and costs.

7. Pay special attention to the fact that when the supplier explains the offer, he will try to increase your understanding of the value, so that you will naturally accept his price.

8. Procurement should also be good at crying poor, if you are always in front of suppliers to thank the attention to procurement practitioners wechat public number put a look of wealth, it is certainly difficult to get a more favorable price.

9. When you need a quotation from a supplier, you must learn to hide your procurement purpose and grasp the needs of procurement. If you tell the supplier what you want in advance and then ask for a quote, the price may be too high. That means it's hard or impossible to get the price you want.

10. To analyze the source of the supplier's raw materials, and improve the cost impact of non-normal factors in the procurement cost model. This helps us analyze the true cost of suppliers.

11. It is necessary to pay attention to the problem that the supplier uses the positive tolerance quotation to calculate the cost and the negative tolerance production. In other words, sometimes when the supplier calculates the procurement cost, all of them are calculated according to positive tolerances, but in fact, all of the products are produced with negative tolerances. The condition of the mold should be evaluated periodically.

twelve Analyze the vendor's proposal for pitfalls. The supplier's suggestions are valuable, but there may be conspiracies against us, we must distinguish the "good intentions" of the supplier.

13. The quotation should specify the brand of the raw material supplier, and the replacement should go through the procurement certification. This can not only avoid the supplier "shoddy", but also control the cost and ensure the quality.

fourteen The review of raw materials should not be relaxed, especially the split offer. Usually suppliers put "water" on raw materials, procurement is also easy to accept, and many procurement in the supplier's raw material cost analysis of this input resources, spend less time, especially the price of raw materials change greatly, suppliers often take the opportunity to raise prices. The raw materials in the supplier's quotation cannot move, which is a wrong view.

Fifteen. Suppliers usually quote the parts of procurement that are most familiar with the cost or the most transparent part of the market. Thank you for paying attention to the wechat public accounts of procurement practitioners to let us think that the quotation of suppliers is real and cheap, and gain the trust of procurement in the quotation of suppliers. Instead, bid up the least familiar parts of the purchase or the parts of the market that are not transparent.

16. Pay attention to the flexible items in the quotation. Supplier quotation often hides a lot of flexible calculation cost items, such a quotation strategy, suppliers can often succeed in obtaining large profits in the future. If you do not pay attention to procurement, you will pay unnecessary costs. Preferably items that reduce the cost of flexible computing.

17. Pay special attention to the cost loss caused by container residues (impurities). In addition to the problem of gas container residue, in fact, the glue that is constantly recycled also has a similar problem.

18. Attention should be paid to the disposal of the waste material generated by the production of the product, and the value generated by it should also be assessed as part of the supplier's profit, or against the cost.

19. A comprehensive review should be conducted to track possible tax changes on purchased products. (Taxes are often double-counted.)

20. Quotation analysis and cost analysis should be combined with supplier factory analysis. Many purchasing managers believe that purchasing to the supplier's factory is a waste of time, and there are travel costs. The most important thing is to purchase to the supplier's factory, which will be easier to be "fixed" by the supplier. Thank you for paying attention to the procurement practitioners wechat public number this view makes many of the company's procurement staff unable to do more professional. Because they have no idea how the products they buy are produced, let alone how much the suppliers cost to provide them.

Twenty-one. Pay special attention to the problem of suppliers cutting corners. The supplier can make whatever you want for whatever you want, just by cutting corners. Low price does not mean low cost, quality and quantity is very important, so we should constantly track and analyze the changes in the quality and quantity of purchased products.

Twenty-two. For the production of plastic parts, casting parts, etc., the ratio of old and new materials should be specially controlled. We might even consider unannounced audits of supplier integrity. Check whether the supplier is producing according to the technical standards specified in the purchase.

23. Attention should be paid to the analysis of items where the cost of the finished product cannot be accounted for or the material consumption can be accounted for.

24. In order to understand the learning curve and scale effects of supplier costs, multi-stage pricing should be used. The more labor-intensive the product, the greater the scope for subsequent cost reduction; The more in the mass production stage, the cost is likely to decline in a learning curve, and the learning curve even lasts a long time. In addition, scale effects are also likely to be an important factor in cost changes. Through the analysis of learning curves and economies of scale tracking and analysis, procurement costs can be automatically reduced.

Twenty-five. Usually, 20% of the items in the quotation often account for 80% of the cost, 30% of the items account for 15% of the cost, and 50% of the items account for only 5% of the cost. So we need to focus on the items that account for the largest share of the total cost.

Twenty-six. Integer items, suppliers are likely to be rough estimates, very rough, should be concerned. In addition, costs such as sales are likely to have economies of scale and need to be linked to the volume of purchases when allocating costs.

27. It should be noted that the supplier uses the psychometric quotation method, which is manifested in two forms: the first form is that the supplier creates a feeling that the quotation is calculated; The second form is that the supplier quotes the price lower than our certain psychological price, so that the procurement is easier to trust and accept. Thank you for paying attention to purchasing practitioners wechat public number

28. The so-called proof provided by the supplier is likely to be second-hand data and information, and do not stop analyzing the supplier's cost because of the proof unless you are really confident that there is no problem.

29. Analyze the rate of allocation of expenses as much as possible, not the addition, subtraction, multiplication and division of expenses. Because distribution rates are relatively easy to compare with industries and suppliers. As mentioned earlier, suppliers often make a fuss about raw materials, in fact, the costs of various projects, including direct wages, manufacturing costs, administrative costs, and financial costs are also of great importance.

Thirty. Logic errors are a problem that we need to pay special attention to, especially for complex projects. Suppliers often make this mistake on purpose.

Thirty-one. The purchase quantity and the economics of the mold should be evaluated.

Thirty-two. The supplier should evaluate the match of the mold developed by the supplier with other suppliers.

Thirty-three. The leverage point of the quotation should be analyzed emphatically, and it should be calculated every ounce.